The Combination Square

man is a builder with a natural desire and an inborn knack for putting things together early in life we find out there are a lot of problems and putting things together right the pieces don't always fit the way we'd like them to takes practice and training before too long we find out about square corners [Music] angles and miters curves in circles and we discover the tools for making sure that the pieces fit together the way they should perhaps the most versatile and useful of these tools is the combination square with this single all-purpose tool we can lay out and check square corners and joints by out and check angles [Music] or find the center of circles and cylinders within the limits of its size its shape and its accuracy the combination square can be used for almost every type of exact measurement the combination square is basically a specialized development of the elementary steel scale and consists of the specially designed blade and three removable adjustable heads the tri square head the protractor head and the center head the blade of a good quality combination square has an easy-to-read non-glare satin finish it comes in a variety of lengths it is marked off in inches and fractions of an inch like a standard steel scale each edge of the blade is graduated to a different degree of accuracy on this side eighth and sixteenth and on the other side thirty seconds and sixty fourths the center Slott in the blade serves as a track for the head each of the heads contains a bolt assembly which acts as a guide for the blade on the blade is reversed the bullet assembly must also be reversed [Music] the heads are locked on the blade by tightening this locking nut the bold assembly in each of the heads works in the same way it's shown here with the center head the most commonly used head attachment is the tri square with its 90 degree square face it's 45 degree miter face and the handy scriber for marking off layout to fit the head attachment and blade together simply loosen the locking nut and slide the head onto the blade the tongue on the locking bolt fits into the slot on the blade if the head doesn't slide on the blade easily don't try to force it check the alignment of the tongue and the slot when the parts are properly lined up they fit together easily the locking bolt is reversible that is it can be rotated from one side to the other without removing it from the head this means that the blade can be easily reversed without having to remove the locking nut and bolt and this is a handy feature for changing from one graduation scale to another say from the sixteenth scale to the thirty second scale the other heads fit onto the blade in the same fashion as the square head let's look at that again this time with a protractor head loosen the nut slide on the head lock it in place with the protractor head you can set any angle from 0 to 180 degrees for laying out work or from measuring or checking angles with a locking nut loosened the face is free to rotate [Music] to select an angle say 32 degrees loosen the locking nut and rotate the revolving turret until the index mark is lined up with the second mark past the 30 that's 30 31 32 degrees now hold the face steady and secure the head with a locking nut and check the reading to make sure it's right after you tighten down with the protractor head set to 32 degrees you have set in a 32 degree angle between the edge of the blade and the face of the protractor head you can also get a 32 degree angle in the other direction by turning the tool over the angle remains the same in addition to the 32 degree angle formed here the angle formed here is equal to 148 degrees the difference between 180 degrees the full half circle and the 32 degree angle set in here most protractor heads are provided with a second set of reverse degree markings to identify this second angle called the supplementary angle any two angles which add up to 180 degrees are called supplement and each time an angle is set in on the protractor head two angles are formed the angle you set in and the supplementary angle most commonly protractor heads have a scale marked off in steps of one degree with identifying numbers every 10 degrees and a longer mark to identify the five degree point between numbers let's take the accessory heads for the combination square one at a time the tri square head the protractor head and the center head and see how they are used to make actual measurements the head you will use most often for most things as the tri square head to lay out square corners the face of the head is placed firmly against the work the blade forms a square line to the face and the scriber is used to mark the layout [Music] the square head is also useful in checking the prunus of square corner joints especially where proper fit is important you can use your square head to be sure the pieces will fit before they are put together here is another example of how the square head is used to check work in progress here a craftsman uses the combination square to check this square joint before he joins the metal he makes the necessary Corrections clamps the work down and he's ready to go after the joint is completed he uses the square again to make sure everything came out alright let's take a look at this small assembly project the drawing calls for these two pieces of sheet metal to be spot welded together we need a one and a half inch right angle Bend put in the vertical piece and then it is to be joined at right angles to the base exactly two and 3/8 inches from the edge and parallel to the edge the first step is to check the square of the pieces and there okay [Music] now he sets his combination square for one and a half inches removes the scriber and moves the tool along the edge of the work describe a line parallel to the edge and exactly one and a half inches from it this shows him where to make the right angle Bend and of course he checks the bend to make sure it's square by scribing a line parallel to the edge and just two and 3/8 inches from it he marks the point where the vertical wall is to be spot welded he checks to be sure the joint is square that the vertical wall is properly spaced from the edge of the base piece he clamps the pieces together ready for spot welding and here is the completed job exactly as specified the mitre face of the tri square head is used exactly like the square face except it is used for measuring and marking 45-degree angles instead of 90-degree angles use it for laying out mitered corners or for any application where a 45-degree angle is needed the center head fits onto the blade in the same fashion as the tri square head the faces of the center head hold the tool in position so that the blade edged passes through the center of the circle for a more exact location scribe the diameter and then move the tool to a new point on the circumference and scribe a short mark across the diameter line where the lines cross is the true Center the technique is the same for cylindrical work position the faces of the head firmly on the circumference of the cylinder and scribed the diameter move the tool to a new position inscribe a cross line to find the center the protractor head functions as a more versatile and more exact variation of the mitre face on the square head with a protractor head any angle from 0 to 180 degrees can be set in 4 layout the desired angle in this case 50 degrees is set in and the tool used to scribe the line as with a tri square head for measuring angles the locking nut is loosened the edge of the blade is held firmly against one face of the angular work and the turret is rotated until the face of the protractor head is flush against the other face of the angle the setting is snugged up by tightening the locking nut and the angle read from the protractor in this case 65 degrees to transfer exact angular measurements combine the measuring and the layout technique measure the angle set the protractor and with the desired angle set in proceed to lay out an exact duplicate angle [Music] a number of pieces of work can be checked for accuracy by setting in the correct angle and using the preset tool as a measuring standard like all precision tools your combination Square will give you better measurements when you give the tool proper care just keep the blade and the heads clean and protect your tool from water and dampness which cause rust store it where it is protected from damage and handle it with reasonable care to keep from damaging or burying the surfaces this then is your combination square the most all-around tool on your bench for layout use your combination square to make perfect square corners or 45 degree miter corners a small spirit level mounted in the Tri square head can be used to check surfaces for level to inspect measure or lay out any angles the protractor head is what you need use it to measure unknown angles or preset a known angle for layout or inspection remember that every time you set in an angle you also said in its supplement [Music] use the center head on circular flat work for cylindrical pieces find centers measure diameters do it all with one tool your combination square